---
title: "Nature of sound and the human ear"
subject: "Environment and Pollution Control"
chapter: 6
key: "semester_7/environment_and_pollution_control:sound-nature-human-ear"
source: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/sound-nature-human-ear
site: BCT Engineering
---

# Nature of sound and the human ear

Environment and Pollution Control · Chapter 6: Noise pollution

- Asked in: year not given, 6 marks
- Video: [Anatomy of the Human Ear](https://www.youtube.com/watch?v=3G5jiXl2LSM) — SMC468 Graphic Design for Education
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/sound-nature-human-ear
- Whole chapter: https://www.bctengineer.com/md/semester_7/environment_and_pollution_control/chapter-6

## Question

Explain the nature of sound (wave properties, frequency, wavelength and speed). With a neat sketch, describe the structure and working of the human ear and state the audible range.

## Short answer

Sound is a longitudinal pressure wave; speed in air ≈343 m/s at 20°C, c=fλ. Audible range 20 Hz–20 kHz. Outer ear directs waves to eardrum; middle ear ossicles (hammer, anvil, stirrup) amplify and transmit to oval window; inner ear cochlea fluid bends hair cells converting vibration to nerve signals. Hair cell damage from loud noise is permanent.

## Answer

#### Nature of sound
Sound is a longitudinal pressure wave that travels through an elastic medium (air, liquid or solid) by alternate compression and rarefaction of particles. It cannot travel in vacuum.

- **Frequency $f$ (Hz):** number of cycles per second. **Time period** $T = 1/f$.
- **Wavelength $\lambda$ (m):** distance between consecutive compressions.
- **Speed $c$:** $c = f\lambda$. In air $c = 331.4 + 0.6\,T$ (T in $^\circ$C) $\approx 343$ m/s at 20 $^\circ$C; about 1480 m/s in water and 5000 m/s in steel.
- **Amplitude** (sound pressure) decides loudness; frequency decides pitch.
- Audible range for a healthy young person: **20 Hz to 20 000 Hz**; below is infrasound, above is ultrasound.

#### Human ear
```text
  Outer ear      Middle ear           Inner ear
 +--------+   +-----------------+   +--------------+
 | pinna  |   |  ossicles       |   |  cochlea     |
 | canal  |-->|  hammer-anvil-  |-->|  (fluid +    |--> auditory
 |   |    |   |  stirrup        |   |  hair cells) |    nerve
 |eardrum |   |  (Eustachian    |   |  semicircular|    to brain
 +--------+   |   tube)         |   |  canals      |
              +-----------------+   +--------------+
```
1. **Outer ear:** pinna collects sound and the ear canal guides it to the eardrum (tympanic membrane), which vibrates.
2. **Middle ear:** three small bones (malleus, incus, stapes) amplify and transmit the vibration to the oval window. The Eustachian tube equalises pressure.
3. **Inner ear:** the fluid-filled cochlea contains the basilar membrane with thousands of hair cells. Vibration makes the fluid move, bending the hair cells that convert it into nerve signals, carried by the auditory nerve to the brain. High frequencies are sensed near the base and low frequencies near the apex of the cochlea. The semicircular canals do not hear but control balance.

Damage to hair cells by loud noise is permanent.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What type of wave is sound?
   A. Transverse electromagnetic wave that can travel in vacuum
   B. Longitudinal pressure wave needing an elastic medium
   C. Transverse wave in solids only
   D. Surface wave in air only
   Answer: B. Sound travels by alternate compression and rarefaction of particles in an elastic medium, so it cannot pass through vacuum. (Key point: Nature of sound)

2. What is the role of the middle ear ossicles (malleus, incus, stapes)?
   A. Convert vibration to nerve signals
   B. Control balance
   C. Collect sound from air
   D. Amplify and transmit eardrum vibration to the oval window
   Answer: D. The three small bones amplify the eardrum vibration and pass it to the oval window of the inner ear. (Key point: Role of ear parts)

3. Where are sound vibrations converted into nerve signals?
   A. In the cochlea, by hair cells on the basilar membrane
   B. In the pinna
   C. In the Eustachian tube
   D. In the semicircular canals
   Answer: A. Fluid movement in the cochlea bends hair cells that generate nerve signals; semicircular canals only control balance. (Key point: Cochlea function)

4. What is the audible range for a healthy young person?
   A. 2 Hz to 2000 Hz
   B. 20 Hz to 20 000 Hz
   C. 200 Hz to 200 000 Hz
   D. 0 Hz to 20 Hz
   Answer: B. Audible range is 20 Hz to 20 kHz; below is infrasound and above is ultrasound. (Key point: Audible range)

## Related in Environment and Pollution Control

- [Typical noise levels and effects of noise](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Anoise-levels-places-effects) — Environment and Pollution Control, chapter 6

## Related in other subjects

- [Audible sound, reflected-sound defects, insulation](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Asound-audible-insulation) — Building Technology, chapter 1
- [Project finance; sound capital structure; factors](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aproject-finance-features-sound-capital-structure) — Project Engineering, chapter 6, asked 2×
- [Features of a sound capital structure](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acapital-structure-features-sound) — Project Engineering, chapter 6
- [Speed of sound and Mach number](https://www.bctengineer.com/question.md?key=semester_4%2Ffluid_mechanics_mechanical%3Amach-number-speed-of-sound-regimes) — Fluid Mechanics, chapter 9